Overview of Female Pelvic Floor Muscle Anatomy and Physiology

Original Editor - Jess Bell based on the course by Ibukun Afolabi
Top Contributors - Jess Bell, Jorge Rodríguez Palomino, Kim Jackson and Rucha Gadgil

This article or area is currently under construction and may only be partially complete. Please come back soon to see the finished work! (5/12/2021)

Introduction

The pelvic floor does not exist in isolation. It is part of a complex system that works synergistically with structures and systems both nearby and further away in the body, including the ankle / foot complex, the thorax and respiratory complex, the central nervous system and the brain. Because the body is a dynamic, interrelated, fascially connected, biotensegral system, it is important that pelvic health physiotherapists consider the contribution of all these systems and structures when assessing and treating pelvic health complaints.

The Pelvic Floor

Health professionals might have differing views about what makes up the pelvic floor:

• Is it just comprised of the pelvic floor muscles?
• Should the pelvic organs be included?
• Is the hip joint part of the pelvic floor?
• Are the contents of the lower abdominal cavity also included?

For the pelvic health physiotherapist, the pelvic floor refers to the area at the bottom of the pelvis and all of its contents, and associated structures, including:

• The pelvis itself
  • Called the pelvic ring or pelvic bowl
  • Includes the pelvic joints
• Pelvic organs
  • The bladder, uterus and rectum in women
• Pelvic ligaments
• The endopelvic fascia and connective tissue
• The nerves which innervate the pelvic region, as well as blood vessels and the lymphatic system
• The external genitalia
• The pelvic floor musculature

Pelvic health physiotherapists are able to treat all these structures either directly or indirectly.

This page focuses on the anatomy of the female pelvic floor musculature. More information on the other structures within the pelvis is available here.

Pelvic Cavity

The abdominal and pelvic cavities are bordered at the front, top, back and bottom:

• The front border is the abdominal wall
• The top border is the respiratory diaphragm
• The back border is the spinal column
• The bottom border consists of the pelvic floor muscles

Pelvic Floor Muscles

The pelvic floor muscles act to close off the bony outlet, which they do so completely apart from specific openings:

• The urogenital hiatus
  • Contains the urethra and vagina in women
  • Positioned anteriorly
• The anal hiatus
  • Contains the anal canal
  • Positioned posteriorly

The muscles of the pelvic floor are divided into three layers.

Deep Layer - Pelvic Diaphragm

The deepest layer of the pelvic floor muscles is known as the pelvic diaphragm. It is a broad, funnel-shaped sling of fascia and muscle suspended from bony anchor points in the lesser pelvis (i.e. the area of the pelvic cavity below the linea terminalis).

The muscles of the pelvic diaphragm are:

• Ischococcygeus muscle (also known as the coccygeus muscle)
  • Originates from the ischial spine and inserts into the lateral aspect of the coccygeal vertebrae
• Levator ani
  • A composite muscle that is traditionally divided into three parts:
    • Pubococcygeus: originates from the internal surface of the pubic ramus and inserts into the lower sacral and coccygeal vertebrae
    • Illiococcygeus: originates at the arcus tendinous levator ani (ATLA) and fuses with the pubococcygeus
    • Puborectalis: originates at the inner surface of the right and left sides of the pubic bone. The two muscles meet behind the rectum and form a continuous sling

In this deep part of the pelvic floor, it is also possible to palpate the obturator internus and piriformis muscles. These muscles are not, however, considered to be part of the pelvic floor diaphragm. Instead, they are rotators of the hip.  

Middle Layer - Urogenital Diaphragm / Perineal Membrane

The middle layer has traditionally been called the urogenital diaphragm, but is often now referred to as the perineal membrane.

There is controversy over whether this layer contains:

• A transverse sheet of muscle called the deep transverse perinei muscle which is between an inferior and superior fascia OR
• Three joined muscles and an inferior fascial layer (i.e. the perineal membrane)

However, the middle layer stretches across the urogenital triangle (see below) and in women, houses the urethral and vaginal sphincters (i.e. the sphincter urethrovaginalis, the external urethral sphincter, and the compressor urethrae). These sphincters close the urethra and vagina, maintaining continence. The entire perineal layer provides additional support for the deeper pelvic floor structures.

Superficial Layer

The most superficial layer of the pelvic floor muscles consists of:

• Bulbocavernosus and ischiocavernosus:
  • These muscles assist with clitoral function during arousal and climax
• Superficial transverse perineal muscles (paired):
  • Provide additional support for the urogenital diaphragm
• External anal sphincter:
  • A circular, layered muscle that closes off the anal canal

The perineum (perineal body) and superficial transverse perineal muscles divide into two triangles:

• Anterior triangle (called the urogenital triangle)
• Posterior triangle (called the anorectal triangle)

Physiology of the Pelvic Floor

The pelvic floor muscles are, in many respects, just like any other skeletal muscle group:

• They can contract and relax
• Be shortened or lengthened
• Be weak or strong
• Be stiff or supple
• They can hold tension or move dynamically
• May be coordinated or lack coordination - within itself or with other muscle groups
• Can be normally regulated or “dysregulated”

The pelvic floor muscles contain both fast- and slow-twitch fibres. Slow-twitch fibres make up 70 percent of the pelvic floor.

The high prevalence of slow-twitch fibres means that these muscles are able to maintain a degree of resting activation. They are, therefore, considered to be postural muscles. This resting activation also enables the maintenance of continence.

The fast-twitch fibres allow the muscles to contract voluntarily when necessary (e.g. during an expected or unexpected increase in intra-abdominal pressure).